Modern developments in physical vapor deposition methodologies have created increasingly stringent requirements for robust bonding between targets and backing plates. A diagrammatic view of a portion of an exemplary sputter deposition apparatus 10 is shown in FIG. 1. Apparatus 10 comprises a backing plate 12 having a sputtering target 14 bonded thereto. A semiconductive material wafer 16 is within apparatus 10 and provided to be spaced from target 14. Sputtered material 18 is displaced from target 14 and utilized to form a coating (not shown) over wafer 16.
Among the modern improvements in sputter design is an increase in the distance between target 14 and semiconductive material substrate 16. Such increase in distance can enable more directional sputtering to be achieved over features of substrate 16 than can be achieved when target 14 is close to substrate 16 by allowing atoms that are not moving perpendicular to substrate 16 to land on the sidewall of the sputtering chamber. Specifically, substrate 16 will frequently have vertical holes or slots (known as vias) with depths five times their width or more (i.e., having relatively high critical dimensions). It is difficult to sputter materials into vias having high critical dimensions unless there is a relatively long throw between a sputtering target and a substrate comprising the vias.
Although the longer throw creates advantages in coverage relative to shorter throw techniques, it also creates complications. One of such complications is caused by additional power utilized in long-throw technologies. The additional power can cause sputtering targets to get hotter than they had in older methods. Such heat can disrupt a bond formed between backing plate 12 and target 14. For instance, if target 14 is solder-bonded to backing plate 12, the heat developed during long-throw sputtering techniques can be sufficient to melt the solder bond and actually break target 14 free from backing plate 12. Accordingly, solder-bonding can be inappropriate for long-throw sputtering techniques.
It would be desirable to develop improved methods for bonding physical vapor deposition targets to backing plates.